The present invention relates to assays and methods for identifying or for testing agents which are modulators of a serine-threonine phosphatase PPM1E and can be used for treating and/or preventing neurodegenerative disorders.
The present invention relates to methods of diagnosing, prognosticating and monitoring the progression of neurodegenerative diseases.
The present invention relates to the treatment and/or prevention of neurodegenerative disorders, more particularly to the treatment and/or prevention of Alzheimer's disease.
Neurodegenerative diseases, in particular Alzheimer's disease (AD), have a strongly debilitating impact on a patient's life. Furthermore, these diseases constitute an enormous health, social, and economic burden. AD is the most common neurodegenerative disease, accounting for about 70% of all dementia cases, and it is probably the most devastating age-related neurodegenerative condition affecting about 10% of the population over 65 years of age and up to 45% over age 85 (Wimo et al., Alzheimer Dis. Assoc. Dis. 2003, 17:63-67; Walsh and Selkoe, Neuron 2004, 44:181-193). Presently, this amounts to an estimated 12 million cases in the US, Europe, and Japan. This situation will inevitably worsen with the demographic increase in the number of old people in developed countries. The neuropathological hallmarks that occur in the brains of individuals with AD are senile plaques, composed of amyloid-β protein, and profound cytoskeletal changes coinciding with the appearance of abnormal filamentous structures and the formation of neurofibrillary tangles (Selkoe and Kopan, Annu Rev Neurosci 2003, 26:565-597; Saido and Iwata, Neurosci. Res. 2006, 54:235-253; Braak and Braak, J Neural Transm 1998, 53: 127-140; Schmitt et al., Neurology 2000, 55: 370-376).
Currently, there is no cure for AD, nor is there an effective treatment to halt the progression of AD or even to diagnose AD ante-mortem with high probability. Although there are rare examples of early-onset AD which have been attributed to genetic defects in the genes for amyloid precursor protein (APP) on chromosome 21, presenilin-1 on chromosome 14, and presenilin-2 on chromosome 1, the prevalent form of late-onset sporadic AD is of hitherto unknown etiologic origin. The late onset and complex pathogenesis of neurodegenerative disorders pose a formidable challenge to the development of therapeutic and diagnostic agents. It is crucial to expand the pool of drug targets and diagnostic markers.
It is therefore an object of the present invention to provide insight into the pathogenesis of neurodegenerative diseases and to provide methods, materials, agents and compositions which are suited inter alia for the diagnosis and the prevention and treatment of these diseases. This object has been solved by the features of the independent claims. The subclaims define preferred embodiments of the present invention.
The present invention discloses the use of a protein phosphatase 1 E (PPM1E) in methods for identifying or for testing agents for the treatment and/or prevention of neurodegenerative diseases and the use of PPM1E in diagnostic methods. A gene of the protein phosphatase 2C superfamily, coding for the protein phosphatase 1 E (PPM1E) and protein products thereof is dysregulated, is differentially expressed in human Alzheimer's disease brain samples. PPM1E has been formerly known as CaM kinase phophatase N (CaMKP-N) or as Partner of PIX 1 (POPX1); such formerly used gene symbols CaMKP-N or POPX1 have been exchanged to PPM1E in accordance with the HUGO (Human Genome Organisation) gene nomenclature.
Protein phosphatases are the counterparts of kinases in a variety of complex regulatory mechanisms of cellular functions like stress-activated signal transduction, mitogenic signal transduction, and cell cycle control. PPM1E is a serine-threonine phosphatase of 755 amino acids (84.0 kDa) that was identified as cDNA KIAA1072 in a project to accumulating basic information of unidentified human genes (Genbank accession number AB028995; REFSEQ accession number NM 014906; Kikuno et al., DNA Res. 1999, 6:197-205). The PPM1E gene is located on chromosome 17q22. PPM1E is also known as partner of PIX (POPX1) (Genbank accession number AF520614; Koh et al., Current Biology 2002, 12:317-321), as PP2CH (Genbank accession number AF260269; unpublished), and in the rat as nuclear calmodulin-dependent protein kinase phosphatase (CaMKP-N) (Genbank accession number AB081729; Takeuchi et al., J. Biochem. 2001, 130:833-840).
PPM1E was identified and characterized as substrate-specific phosphatase that dephosphorylates and concomitantly deactivates Ca2+/calmodulin-dependent protein kinases (CaMKs) such as CaMKI, CaMKII, and CaMKIV (Takeuchi et al., J. Biochem. 2001, 130:833-840). Enzymatic activity of PPM1E requires Mn2+ ions and is activated by polycations (Takeuchi et al., J. Biochem. 2001, 130:833-840; Ishida et al., Arch. Biochem. Biophys. 2002, 408:229-238). PPM1E was shown to be specifically expressed in brain (Takeuchi et al., J. Biochem. 2001, 130:833-840); in rat neurons PPM1E is present in the nucleus, in the cytoplasm and concentrated at synaptic sites (Kitani et al., J. Neurochem. 2006, 96:374-384). PPM1E exists in two forms, as full length protein carrying different nuclear localization signals at the C-terminus (Takeuchi et al., J. Biochem. 2004, 136:183-188), as well as a posttranslationally C-terminal truncated form of the full-length protein lacking amino acids 568-766 which include a nuclear localization signal (Kitani et al., J. Neurochem. 2006, 96:374-384). In addition to the CaMK-specific phosphatase activity it is reported that PPM1E forms a complex with Rho guanine nucleotide exchange factor 6 (ARHGEF6) and Serine/threonine-protein kinase PAK 1 (PAK1) and thereby antagonizes cdc42-mediated activation of PAK1 (Koh et al., Current Biology 2002, 12:317-321). A relation of PPM1E with neurodegenerative diseases, in particular with Alzheimer's disease, has not been disclosed so far.